Hot-melt adhesive having improved bonding strength

ABSTRACT

Hot-melt, pressure-sensitive adhesive compositions of amorphous polyalphaolefin and crystalline polypropylene have improved bond strength over the amorphous polyalphaolefin alone. The adhesive compositions improve dynamic shear strength, dynamic peel strength, as well as static peel strength. The adhesive compositions are particularly suitable for use in absorbent articles.

This application claims benefit of Provisional No. 60/259,037 filed Dec.29, 2000.

BACKGROUND OF THE INVENTION

People rely on disposable absorbent articles to make their lives easier.Disposable absorbent articles, such as adult incontinence articles anddiapers, are generally manufactured by combining several components.These components typically include a liquid-permeable topsheet; aliquid-impermeable backsheet attached to the topsheet; and an absorbentcore located between the topsheet and the backsheet. When the disposablearticle is worn, the liquid-permeable topsheet is positioned next to thebody of the wearer. The topsheet allows passage of bodily fluids intothe absorbent core. The liquid-impermeable backsheet helps preventleakage of fluids held in the absorbent core. The absorbent coregenerally is designed to have desirable physical properties, e.g. a highabsorbent capacity and high absorption rate, so that bodily fluids canbe transported from the skin of the wearer into the disposable absorbentarticle.

Frequently one or more components of a disposable absorbent article areadhesively bonded together. For example, adhesives have been used tobond individual layers of the absorbent article, such as the topsheet(also known as, for example, the body-side liner) and backsheet (alsoknown as, for example, the outer cover), together. Adhesives have alsobeen used to bond discrete pieces, such as fasteners and leg elastics,to the article. In many cases, the bonding together of components formsa laminated structure in which adhesive is sandwiched between materials(such as layers of polymer film and/or layers of woven or nonwovenfabrics) that make up the components being bonded together.

In many instances, a hot-melt adhesive, i.e. a polymeric formulationthat is heated to substantially liquefy the formulation prior toapplication to one or both materials when making a laminate, is used inmaking a laminated structure. While such formulations generally work,they can be costly and their performance properties can be improved. Forexample, adhesion can be improved to help provide a sturdier laminate(e.g., to improve the integrity or strength of the bond between twocomponents in a disposable absorbent article).

There is a need or desire for an adhesive composition that possesses oneor more performance characteristics that are comparable to, or betterthan, one or more of the same performance characteristics (e.g., bondstrength) of a conventional hot-melt adhesive and that will typicallycost less than a conventional hot-melt adhesive. Laminated structuresand disposable absorbent articles employing the adhesive compositionwould benefit from these improved characteristics. There is also a needor desire for efficient methods of making the adhesive composition, andefficient methods of making laminated structures and disposableabsorbent articles employing the adhesive composition.

SUMMARY OF THE INVENTION

The present invention is generally directed to amorphous polyalphaolefinadhesive compositions having improved bonding strength through theaddition of crystalline polypropylene. The adhesive compositions havebetter performance characteristics, e.g. shear and peel bondingstrengths, than conventional hot-melt adhesives, and may cost less thanconventional hot-melt adhesives.

The combination of amorphous polyalphaolefin (APAO) and crystallinepolypropylene possesses desirable adhesive properties and may be used tomake laminated structures and disposable absorbent articles. Theadhesive compositions of the invention can be applied to a wide varietyof substrates, including nonwoven webs, woven webs, and films. Theadhesive can be applied in a swirl pattern, can be melt-blown, or can beapplied using any technique suitable for hot-melt adhesives.

Without being bound to any particular theory, it appears that such agreat difference between bonding strength of the adhesive compositionsof the invention and conventional amorphous polyalphaolefin adhesivesmay be attributed to crystallization of crystalline, or isotactic,polypropylene, which generates physical intermolecular linking in thematrix of APAO.

As stated above, a material comprising a combination of an APAO andcrystalline polypropylene may cost less than a conventional hot-meltadhesive. Generally this is because conventional hot-melt adhesives aretypically formulated by combining several components, including apolymer or polymers for cohesive strength; resins, tackifiers, or othergenerally low molecular-weight materials for adhesive strength;viscosity modifiers such as oils or wax-like materials; and otheradditives (e.g., antioxidants). In some versions of the invention, acombination of the APAO and crystalline polypropylene alone providesimproved bond characteristics compared to conventional hot-meltadhesives. But it should be understood that the invention encompassesadhesive compositions that include selected amorphous polyalphaolefinsand crystalline polypropylenes, combined with other additives ormaterials.

Another advantage present in some versions of the invention is that thematerial of the invention may be used in conventional hot-melt-adhesiveprocessing equipment. Thus, the adhesive material may be used inequipment already installed for the purpose of processing and applyingconventional hot-melt adhesives.

Apart from whether or not adhesive compositions of the present inventioncost less than conventional hot-melt adhesives, we have found thatrepresentative embodiments of the present invention possess improvedperformance characteristics compared to the performance characteristicsof conventional hot-melt adhesives. These performance benefits mayjustify processing and applying adhesive compositions of the presentinvention in modified conventional-hot-melt-adhesive equipment, or inequipment especially designed and built for the purpose of processingand applying adhesive compositions of the present invention.Furthermore, these performance benefits may justify adhesivecompositions of the present invention, in some instances, being at ahigher cost than conventional-hot-melt adhesives.

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 gives symbolic representations of syndiotactic, isotactic, andatactic configurations of a polymer.

FIG. 2 gives a visual representation of a fringed-micelle model of amaterial having both amorphous and crystalline regions.

FIG. 3 shows a schematic diagram of one version of a method andapparatus for preparing, processing, and delivering an adhesivecomposition.

FIG. 4A shows one version of a feedback control scheme.

FIG. 4B shows one version of a feedforward control scheme.

FIG. 5 shows one version of a process control system.

FIG. 6 shows one version of a process for making a laminate comprisingan adhesive composition.

FIG. 7A shows a top view of a portion of one version of a laminate.

FIG. 7B shows a sectional, perspective view of a test panel cut from oneversion of a laminate.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The present invention is generally directed to adhesive compositionscomprising amorphous polyalphaolefin (APAO) and crystallinepolypropylene. Adhesive compositions of the present invention generallyperform better, and typically cost less, than conventional hot-meltadhesives. Furthermore, these compositions may typically be processedand applied using conventional hot-melt adhesive processing equipment.Generally new equipment will not be necessary to use adhesivecompositions of the present invention.

Before describing representative embodiments of the invention, it isuseful to define a number of terms for purposes of this application.These definitions are provided to assist the reader of this document.

“Nonwoven” fabric or web means a web having a structure of individualfibers or threads that are interlaid, but not in a regular oridentifiable manner as in a knitted fabric. Nonwoven fabrics or webshave been formed from many processes such as, for example, meltblowingprocesses, spunbonding processes, air laying processes, and bondedcarded web processes. The basis weight of nonwoven fabrics is usuallyexpressed in ounces of material per square yard (osy) or grams persquare meter (gsm) and the fiber diameters are usually expressed inmicrons. (Note: to convert from osy to gsm, multiply osy by 33.91.)

“Woven” fabric or web means a fabric or web containing a structure offibers, filaments, or yams, which are arranged in an orderly,inter-engaged fashion. Woven fabrics typically contain inter-engagedfibers in a “warp” and “fill” direction. The warp direction correspondsto the length of the fabric while the fill direction corresponds to thewidth of the fabric. Woven fabrics can be made, for example, on avariety of looms including, but not limited to, shuttle looms, rapierlooms, projectile looms, air jet looms, and water jet looms.

“Spunbonded fibers”, or “spundbond fibers”, means small-diameter fibersthat are typically formed by extruding molten thermoplastic material asfilaments from a plurality of fine capillaries of a spinneret having acircular or other configuration, with the diameter of the extrudedfilaments then being rapidly reduced as by, for example, in U.S. Pat.No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschneret al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos.3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman,U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No. 3,542,615 to Doboet al., each of which is incorporated by reference in its entirety andin a manner consistent with the present document. Spunbond fibers arequenched and generally not tacky when they are deposited onto acollecting surface. Spunbond fibers are generally continuous and oftenhave average diameters larger than about 7 microns, and moreparticularly between about 10 and 30 microns. A spunbond material,layer, or substrate comprises spunbonded (or spunbond) fibers.

The term “meltblown fibers” means fibers formed by extruding a moltenmaterial, typically thermoplastic in nature, through a plurality offine, usually circular, die capillaries as molten threads or filamentsinto converging high-velocity heated gas (e.g., air) streams thatattenuate the filaments of molten material to reduce their diameter,which may be to microfiber diameter. Thereafter, the meltblown fibersare carried by the high-velocity gas stream and are deposited on acollecting surface to form a web of randomly dispersed meltblown fibers.Such a process is disclosed for example, in U.S. Pat. No. 3,849,241 toButin. Meltblown fibers are microfibers which may be continuous ordiscontinuous, are generally smaller than 10 microns in diameter, andare generally self-bonding when deposited onto a collecting surface.

As used herein, the term “microfibers” means small-diameter fibershaving an average diameter not greater than about 100 microns, forexample, having a diameter of from about 0.5 microns to about 50microns, more specifically microfibers may also have an average diameterof from about 1 micron to about 20 microns. Microfibers having anaverage diameter of about 3 microns or less are commonly referred to asultra-fine microfibers. A description of an exemplary process of makingultra-fine microfibers may be found in, for example, U.S. Pat. No.5,213,881, entitled “A Nonwoven Web With Improved Barrier Properties”.

“Amorphous polyalphaolefin” refers to a polymer that can include randomcopolymers or terpolymers of ethylene, propylene, and butene, and othersubstantially amorphous or semi-crystalline propylene-ethylene polymers.Suitably, the amorphous polyalphaolefin (APAO) includes between about20% and about 80% copolymers or terpolymers and between about 20% andabout 80% other substantially amorphous or semi-crystallinepropylene-ethylene polymers. Alternatively the APAO includes betweenabout 30% and about 70% copolymers or terpolymers and between about 30%and about 70% other substantially amorphous or semi-crystallinepropylene-ethylene polymers. As yet another alternative, the APAOincludes between about 40% and about 60% copolymers or terpolymers andbetween about 40% and about 60% other substantially amorphous orsemi-crystalline propylene-ethylene polymers.

“Crystalline polypropylene” refers to certain homopolymer polypropyleneshaving at least 40% crystallinity, as well as certain polypropylenecopolymers having at least 40% crystallinity.

“Conventional hot-melt adhesive” means a formulation that generallycomprises several components. These components typically include one ormore polymers to provide cohesive strength (e.g., aliphatic polyolefinssuch as poly (ethylene-co-propylene) copolymer; ethylene vinyl acetatecopolymers; styrene-butadiene or styrene-isoprene block copolymers;etc.); a resin or analogous material (sometimes called a tackifier) toprovide adhesive strength (e.g., hydrocarbons distilled from petroleumdistillates; rosins and/or rosin esters; terpenes derived, for example,from wood or citrus, etc.); perhaps waxes, plasticizers or othermaterials to modify viscosity (i.e., flowability) (examples of suchmaterials include, but are not limited to, mineral oil, polybutene,paraffin oils, ester oils, and the like); and/or other additivesincluding, but not limited to, antioxidants or other stabilizers. Atypical hot-melt adhesive formulation might contain from about 15 toabout 35 weight percent cohesive strength polymer or polymers; fromabout 50 to about 65 weight percent resin or other tackifier ortackifiers; from more than zero to about 30 weight percent plasticizeror other viscosity modifier; and optionally less than about 1 weightpercent stabilizer or other additive. It should be understood that otheradhesive formulations comprising different weight percentages of thesecomponents are possible.

While certain versions of the present invention encompass combinationsof an APAO and crystalline polypropylene only, it should be understoodthat other embodiments of the present invention comprise components inaddition to combinations of APAO and crystalline polypropylene.

“Hot-melt processable” means that an adhesive composition may beliquefied using a hot-melt tank (i.e., a system in which the compositionis heated so that it is substantially in liquid form) and transportedvia a pump (e.g., a gear pump or positive-displacement pump) from thetank to the point of application proximate a substrate or othermaterial; or to another tank, system, or unit operation (e.g., aseparate system, which may include an additional pump or pumps, fordelivering the adhesive to the point of application). Hot-melt tanksused to substantially liquefy a hot-melt adhesive typically operate in arange from about 100 degrees Fahrenheit to about 450 degrees Fahrenheit.Generally, at the point of application, the substantially liquefiedadhesive composition will pass through a nozzle or bank of nozzles, butmay pass through some other mechanical element such as a slot. Ahot-melt processable adhesive composition is to be contrasted with acomposition that requires a conventional extruder, and the attendantpressures and temperatures characteristic of an extruder, to liquefy,mix, and/or convey the composition. While a hot-melt tank and pump in ahot-melt processing system can handle adhesive-composition viscositiesin a range from about 1000 centipoise to about 10,000 centipoise, anextruder can handle and process adhesive-composition viscosities in arange from about 10,000 centipoise to viscosities of several hundredthousand centipoise. An advantage of some adhesive compositions of thepresent invention is that the compositions are hot-melt processable;i.e., the combination of APAO and crystalline polypropylene may besubstantially liquefied in a hot-melt tank and conveyed to the point ofapplication via a pump. As was stated above, however, some adhesivecompositions of the present invention may not possess this particularadvantage.

Unless otherwise noted, “Laminated structure” or “laminate” means astructure in which one layer, material, component, web, or substrate isadhesively bonded, at least in part, to another layer, material,component, web, or substrate. As stated elsewhere in this application, alayer, material, component, web, or substrate may be folded over andadhesively bonded to itself to form a “laminated structure” or“laminate.”

“Polymer”, as used herein, generally includes, but is not limited to,homopolymers, copolymers, such as, for example, block, graft, random andalternating copolymers, terpolymers, and blends and modificationsthereof. As is explained in this document, polymers may assume differentconfigurations, including isotactic, atactic, and syndiotacticconfigurations. “Configuration” describes those arrangements of atomsthat cannot be altered except by breaking and reforming primary chemicalbonds (i.e., covalent bonds). In contrast, “conformation” describesarrangements that can be altered by rotating groups of atoms aroundsingle bonds. It should be noted that a single polymer chain may besynthesized such that some portions of the chain have an isotacticconfiguration and some portions of the chain have an atacticconfiguration.

A graphic example provides additional detail on the types ofconfigurations mentioned above. If a polymer chain is depicted in afully-extended, planar, zigzag conformation 1100, the configurationresulting when all the substituent groups R 1102 on the polymer lieabove (depicted in FIG. 1B) or below (not depicted) the plane of themain chain is called “isotactic”. If substituent groups lie alternatelyabove and below the plane the configuration is called “syndiotactic”(depicted in FIG. 1A). And a random sequence of substituents lying aboveand below the plane is described as an “atactic” configuration (depictedin FIG. 1C). A polymer, or a region of a polymer, having an isotacticconfiguration is more likely to assume characteristics of a crystallinestructure. Pure isotactic polymers are rare. For purposes of thisinvention, the term “isotactic polymer” refers to a polymer that is atleast 60% isotactic, suitably at least 70% isotactic, alternatively atleast 80% isotactic. A polymer, or a region of a polymer, having anatactic configuration is more likely to assume characteristics of anamorphous structure. An atactic polymer may assume some crystallinity,but the degree of crystallinity is typically less than 20%, or less than15%. For purposes of this invention, the term “atactic polymer” refersto a polymer that may not be 100% atactic, but is at least 90% atactic.Similarly, for the purposes of this invention, the term “amorphouspolymer” may assume some crystallinity, but the degree of crystallinityis typically less than 20% or less than 15%. And a polymer, or a regionof a polymer, having a syndiotactic configuration can assumecharacteristics of a crystalline structure, but to a degree less thanthe degree of crystallinity in an isotactic configuration.

In this application, “fringed-micelle model” means a theoreticalconstruct characterizing polymeric structures that have both crystalline150 and amorphous 152 regions (one version of a graphic depiction of afringed-micellar structure is presented in FIG. 2). This model may beused to characterize the structure of an atactic polymer and anisotactic polymer individually, i.e., each polymer possesses bothcrystalline regions and amorphous regions. As explained above, theisotactic polymer likely possesses a greater degree of crystallinitycompared to an atactic polymer. Furthermore, this model may be used tocharacterize the structure of a blend of isotactic polymer and atacticpolymer. It should be understood that this model provides one possibleview of characteristics of the present invention and in no way limitsthe scope thereof.

One version of an adhesive composition possessing features of thepresent invention comprises an APAO, such as a butene-1 copolymer withethylene or propylene, or a butene-1 terpolymer with ethylene andpropylene, having a number-average molecular weight of from about 5,000to about 30,000, specifically about 10,000 to about 20,000. The butene-1copolymer should include about 20% to about 65% by weight butene-1, orabout 30% to about 55% by weight butene-1, and a balance of thecomonomer or comonomers. Alternatively, the APAO may include anethylene-propylene copolymer having up to 80% ethylene. An example of acommercially available APAO suitable for use in the invention is REXTAC®2730, or RT 2730, available from Huntsman Corporation, Salt Lake City,Utah.

The composition also includes crystalline polypropylene having a degreeof crystallinity of about 40% or more, specifically of about 60% ormore, particularly of about 80% or more, and a number-average molecularweight of from about 3000 to about 200,000, more particularly of about10,000 to about 100,000. An example of a commercially availablecrystalline polypropylene suitable for use in the invention is isotacticpolypropylene, available from Sigma-Aldrich. The crystallinepolypropylene may also include syndiotactic polypropylene, orcombinations of isotactic and syndiotactic polypropylene. The adhesivecomposition is hot-melt processable at a temperature of about 450degrees Fahrenheit or less, specifically at a temperature of about 400degrees Fahrenheit or less, particularly at a temperature of about 375degrees Fahrenheit or less, and suitably at a temperature of about 350degrees Fahrenheit or less.

This adhesive composition can have a melt index between about 200 andabout 2000 grams per 10 minutes, or between about 400 and about 1800grams per 10 minutes, or between about 500 and about 1500 grams per 10minutes, as determined using ASTM D 1238, 230° C./2.16 kg Method. Themelt index is dependent upon the crystallinity, molecular weight, andthe molecular weight distribution of the polymers included in theadhesive composition.

In some versions of the invention, the APAO is present in an amount ofabout 70 to about 90 weight percent and the crystalline polypropylene ispresent in an amount of about 10 to about 30 weight percent. In anotherembodiment of the invention, the APAO is present in an amount of about73 to about 87 weight percent and the crystalline polypropylene ispresent in an amount of about 13 to about 27 weight percent. In yetanother embodiment of the invention, the APAO is present in an amount ofabout 75 to about 85 weight percent and the crystalline polypropylene ispresent in an amount of about 15 to about 25 weight percent. Forpurposes of this invention, weight percent is defined as the mass of onetype of polymer (e.g., APAO) in the adhesive composition divided by thesum of the masses of other types of polymer (e.g., APAO and crystallinepolypropylene) in the adhesive composition, plus the mass(es) of anyadditional component(s) that might be present in the adhesivecomposition, with this value being multiplied by 100. So, for example,if we form an adhesive composition comprising 80 grams of APAO with 20grams of crystalline polypropylene, the combination includes 80 weightpercent APAO.

In another aspect, the invention encompasses laminated structuresemploying embodiments of the adhesive composition as described above.For example, one version of a laminated structure of the presentinvention comprises a first layer and a second layer, wherein at least aportion of the first layer is attached to at least a portion of thesecond layer using an adhesive composition that is the same as, oranalogous to, one or more of the embodiments described above, andwherein the laminated structure has improved dynamic peel strength,improved dynamic shear strength, and improved static-peel-failure time,relative to conventional hot-melt adhesive compositions.

For any of the laminated structures described above, the first andsecond layer may be part of one-and-the-same substrate. That is, thesubstrate may be folded over and joined to itself using an adhesivecomposition of the present invention.

Furthermore, the first layer, second layer, or both may comprise avariety of materials, including, but not limited to a nonwoven (e.g., anecked-bonded laminate or a spun-bond material); a film; a wovenmaterial; a substrate comprising cellulosic material, thermoplasticmaterial, or both; some combination of these; or the like.

In yet another aspect, an absorbent article may be formed that employsan adhesive composition of the present invention and/or a laminatedstructure of the present invention. So, for example, one version of anabsorbent article of the present invention comprises a liquid-permeabletopsheet; a liquid-impermeable backsheet; and a laminated structurehaving features of the present invention, such as one or more of theversions described above. Some or all of the backsheet may include thelaminated structure; some or all of the topsheet may include thelaminated structure; the laminated structure may be attached, directlyor indirectly, to the backsheet, the topsheet, or both; or a laminatedstructure or structures may be present in some combination of these.

In addition to various versions of adhesive compositions, laminatedstructures, and absorbent products of the present invention, the presentinvention also encompasses methods of making these compositions,structures, and articles of manufacture.

One version of a method of making a laminated structure having featuresof the present invention comprises the steps of providing a firstsubstrate; providing a second substrate; providing an APAO having aweight-average molecular weight of from about 20,000 to about 60,000,specifically about 25,000 to about 50,000; and providing an isotacticpolypropylene, namely a crystalline polypropylene having a degree ofcrystallinity of about 40% or more, specifically of about 60% or more,particularly of about 80% or more, and a weight-average molecular weightof from about 20,000 to about 300,000, more particularly of about 35,000to about 200,000. The APAO and the crystalline polypropylene are heatedso that they are sufficiently liquefied for blending. The heated APAOand the heated crystalline polypropylene are blended to form an adhesivecomposition that is melt-processable at a temperature of less than about450 degrees Fahrenheit, specifically of less than about 400 degreesFahrenheit, particularly of less than about 375 degrees Fahrenheit, andsuitably of less than about 350 degrees Fahrenheit. The adhesivecomposition is applied to the first substrate, the second substrate, orboth substrates. At least a portion of the first substrate is joined toat least a portion of the second substrate so that some or all of theapplied adhesive composition is positioned between the first substrateand second substrate.

In some methods of the present invention, the APAO is present in anamount of about 70 to about 90 weight percent and the crystallinepolypropylene is present in an amount of about 10 to about 30 weightpercent. In other methods of the invention, the APAO is present in anamount of about 73 to about 87 weight percent and the crystallinepolypropylene is present in an amount of about 13 to about 27 weightpercent. In still other embodiments of the invention, the APAO ispresent in an amount of about 75 to about 85 weight percent and thecrystalline polypropylene is present in an amount of about 15 to about25 weight percent.

It should be understood that the APAO and crystalline polypropylenecould be heated and blended at a site other than the site where thelaminate is being formed. For example, APAO and crystallinepolypropylene could be blended using an extruder/sigma blade mixer orhot-melt processing equipment at a first geographic location. The blendcould then be allowed to cool and processed to make a solid form (e.g.,block or brick). The APAO/crystalline polypropylene blend, in solidform, could then be shipped from the first geographic site to a sitewhere a laminate is to be made. The blend, in solid form, would simplybe heated to substantially liquefy the adhesive composition prior to itsbeing used to make a laminate.

It should also be understood that a method having features of thepresent invention encompasses different sequences of steps by which theadhesive composition is made. For example, the APAO could be heated in afirst container. The crystalline polypropylene could be heated in asecond container, before, after, or concurrently with the heating of theAPAO. Then, the two substantially liquefied polymers could be blended inthe first container, the second container, or a third container.Alternatively, one of an APAO or crystalline polypropylene could beheated in a container, and after the selected polymer is substantiallyliquefied, the remaining polymer could be added to the same container tobe heated and blended. In another alternative, the APAO and crystallinepolypropylene could be added to the same container to be heated andblended at the same time. In other words, our invention contemplatesvarious methods and sequences by which selected amounts of APAO andcrystalline polypropylene (plus any other optional additives) are heatedand blended to form an adhesive composition of the present invention.

The preceding discussion assumes that the APAO and crystallinepolypropylene are in substantially solid form at room temperature, ortemperatures that are typically present in a working environmentsuitable for human beings. To the extent that the APAO or crystallinepolypropylene is available in substantially liquid form, then thosesteps providing for heating and liquefying that material (i.e., thealready-liquefied material) can be omitted from methods of the presentinvention.

A method of making an adhesive composition having features of thepresent invention comprises the steps of providing an APAO having aweight-average molecular weight of from about 20,000 to about 60,000,specifically about 25,000 to about 50,000, and providing an isotacticpolypropylene, namely a crystalline polypropylene having a degree ofcrystallinity of about 40% or more, specifically of about 60% or more,particularly of about 80% or more, and a number-average molecular weightof from about 3000 to about 200,000, more particularly of about 10,000to about 100,000. The APAO and the crystalline polypropylene are heatedso that they are sufficiently liquefied for blending. The heated APAOand the heated crystalline polypropylene are blended to form an adhesivecomposition that is melt-processable at a temperature of less than about450 degrees Fahrenheit, specifically of less than about 400 degreesFahrenheit, particularly of less than about 375 degrees Fahrenheit, andsuitably of less than about 350 degrees Fahrenheit.

In some methods of the present invention, the APAO is present in anamount of about 70 to about 90 weight percent and the crystallinepolypropylene is present in an amount of about 10 to about 30 weightpercent. In other methods of the invention, the APAO is present in anamount of about 73 to about 87 weight percent and the crystallinepolypropylene is present in an amount of about 13 to about 27 weightpercent. In still other embodiments of the invention, the APAO ispresent in an amount of about 75 to about 85 weight percent and thecrystalline polypropylene is present in an amount of about 15 to about25 weight percent.

One version of a method in which an adhesive composition of the presentinvention is metered or delivered at a desired rate to a unit operation(e.g., a unit operation where the adhesive composition is applied to asubstrate or substrates in order to make a laminate) comprises the stepsof: determining the amount of adhesive composition being used by theunit operation per unit time; and force-adjusting the volumetric flowrate or the mass flow rate of the adhesive composition so that theamount of adhesive composition being metered or delivered to the unitoperation corresponds to the amount of adhesive composition being usedby the unit operation per unit time.

In the process description that follows, the preparation, processing,and application of an adhesive composition including APAO andcrystalline polypropylene is described. It should be understood,however, that this description is given as an example. Other processingmethods and equipment may be used to prepare and deliver variousadhesive compositions of the present invention.

FIG. 3 shows a schematic diagram of an apparatus 20, and a method forspraying an adhesive composition, on a moving web 22. The apparatus 20may include a programmable control system 24 that is operativelyconnected to a flow-control system 26. The combination of theprogrammable control system 24 and the flow-control system 26 areconfigured to control the delivery of an adhesive composition in liquidform to the moving web 22. Generally an adhesive composition is receivedin solid form at a manufacturing site where equipment such as thatdepicted in FIG. 3 is located. For example, hot-melt adhesivecompositions may be received as solid pellets, blocks, or some othershape. The solid is then heated so that the hot-melt adhesivecomposition is in a form such that it can be conveyed, and applied, to asubstrate or other material. Usually this requires that the heatedhot-melt adhesive be in substantially liquid form. For the presentinvention, an adhesive composition comprising an APAO and crystallinepolypropylene (e.g., butene-1 copolymer and crystalline polypropylene),in solid form, might be received at a manufacturing site for heating andprocessing as described above. Alternatively, the APAO and crystallinepolypropylene might be received as separate components to be blended atthe manufacturing site. As discussed above, the present inventionencompasses a variety of sequences of steps for making adhesivecompositions of the present invention. An example of equipment andmethods for heating an adhesive composition, or precursor materials tothe adhesive composition, are described in more detail below.

The apparatus may also include a position-sensing system that isconfigured to sense a position of the moving web 22 and, in responsethereto, generate a signal that is sent to the programmable controlsystem 24.

As representatively illustrated in FIG. 3, the continuously moving web22 may be supplied by any means known to those skilled in the art, suchas known conveyor systems. The continuously moving web 22 can includeany type of layer or web of material, such as films, nonwoven webs,woven webs which may include strands of thermoplastic material; naturalmaterial such as threads of cotton and the like, laminate materials, orcombinations thereof. More particularly, the continuously moving web 22may include a necked-bonded laminate (“NBL”), which generally comprisesa polyethylene layer sandwiched between two polypropylene, spunbondedlayers; a polypropylene, spunbonded layer (“SB”); or an outercovercomprising a polyethylene layer and a polypropylene, spunbonded layer.For additional detail on how NBLs and other neck-bonded materials areformed, see U.S. Pat. No. 5,336,545 to Morman, entitled “CompositeElastic Necked-Bonded Material,” which is hereby incorporated byreference in its entirety in a manner consistent with the presentdocument.

As is described below in more specific terms, the adhesive is sprayed onthe continuously moving web 22 in a specific design or pattern forsubsequent placement of or bonding to another material. The othermaterial can be the same or different than the web to which adhesive wasapplied. In some cases adhesive might be applied to both substratesbefore they are joined together. And, as mentioned above, one substratemight be folded over and attached to itself to form a laminatedstructure.

The programmable control system 24 of the present invention isconfigured to send signals to the flow control system 26 which, inresponse thereto, is configured to initiate a spray of adhesive at thecorrect time to provide the desired pattern of adhesive on the movingweb 22. As representatively illustrated in FIG. 3, the flow controlsystem 26 includes an adhesive source 28 which is configured to deliveran adhesive through an adhesive supply line 30 to a metering mechanism32. The adhesive can be delivered to the metering mechanism 32 by anymeans known to those skilled in the art, such as by the use of a pump.

The metering mechanism 32 is configured to continuously supply at leastone independent, volumetric flow of adhesive to a respective nozzle. Asused herein, the term “volumetric flow” refers to a flow of adhesivethat has a predetermined volumetric flow rate. Such a “volumetric flow”may be provided by a positive-displacement metering pump which isconfigured to supply a specific volumetric flow which is independent ofthe manner in which the adhesive is supplied to the metering mechanism32. As a result, for an adhesive that is at a given density, themetering mechanism 32 is configured to provide an independent,predetermined mass flow rate of adhesive to each nozzle. Other adhesiveprocessing and delivery systems utilize pressure to provide a flow ofadhesive.

The metering mechanism 32 of the present invention may be configured tosupply a single, volumetric flow of adhesive to one nozzle or anindependent, volumetric flow of adhesive to each of a plurality ofnozzles depending upon the number of nozzles required to provide thedesired pattern of adhesive on the moving web 22. A suitable device toprovide the metering mechanism 32 may include a positive-displacementmetering pump which is commercially available from May CoatingTechnologies, Acumeter Division, a business having offices located inHolliston, Mass., under the trade designation No. 19539. The meteringmechanism 32 may include any other piston pump or gear pump which arewell known to those skilled in the art.

The metering mechanism 32 may be configured to supply any desiredvolumetric flow rate of adhesive to each nozzle. For example, themetering mechanism 32 may be configured to provide a pre-determinedvolumetric flow rate of from about 1 to about 1000 cubic centimeters perminute and suitably from about 30 to about 180 cubic centimeters ofadhesive per minute to each nozzle. The metering mechanism 32 may beconfigured to provide either a constant or a variable volumetric flowrate of adhesive to each nozzle. For example, if the metering mechanism32 is a positive-displacement metering pump, the speed of the pump maybe controlled to vary the volumetric flow rate of adhesive to thenozzles.

Each nozzle 38 and 40 as representatively illustrated in FIG. 3 can beany device which is capable of providing the desired pattern of adhesiveon the moving web 22. For example, one suitable nozzle is commerciallyavailable from Nordson Corporation, a business having offices located inDuluth, Ga., under the trade designation Model No. 144906. Anothersuitable nozzle for use in the present invention is obtainable from ITWDynatec Co. of Hendersonville, Tenn., under the trade designation number057B1639,1.D. #A3. Such nozzles are typically configured to be operatedbetween an on position and an off position to control the spray ofadhesive from the nozzles. When operated in the on position, each nozzlemay be configured to spray substantially the entire volumetric flow ofadhesive which is independently supplied to it to more accuratelycontrol the amount and pattern of the adhesive on the moving web. Thenozzles 38 and 40 may further be configured to include air streams thatcan be directed to provide a desired pattern in the spray of adhesivebeing dispensed from each nozzle. Such air streams can provide a desiredadhesive spray pattern, such as a pattern of swirls of adhesive. Theadhesive can be applied to the moving web 22 in a concentration ofbetween about 1 gram per square meter (gsm) and about 50 gsm, or betweenabout 5 gsm and about 20 gsm.

After the pattern of adhesive has been sprayed on the moving web 22, theweb may be further processed in a variety of ways. For example, thecontinuously moving web 22 may be contacted by a second substrate web,such as a nonwoven layer, between a pair of nip rolls to adhesively jointhe two substrate webs together. Thereafter, this composite material orlaminate may be used in a variety of ways such as in the construction ofdisposable absorbent articles such as diapers, incontinent articles,training pants, feminine care articles and the like.

The above discussion provides one example of hot-melt processingequipment 15 and a system for applying adhesive to a substrate. Itshould be understood that this is but one example, and that the presentinvention encompasses other systems for preparing and applying adhesives(see, e.g., U.S. Pat. No. 4,949,668, entitled “Apparatus for SprayedAdhesive Diaper Construction,” which issued on Aug. 21, 1990, and whichis hereby incorporated by reference in its entirety and in a mannerconsistent with the present document).

Regardless of the system used to apply the adhesive, the resultingcomposite material or laminate may be exposed to thermal, infrared,ultrasonic, or other forms of energy in subsequent unit operations orprocessing steps. For example, the laminate or composite material maypass through an ultrasonic-bonding unit operation wherein the laminateor composite material are exposed to ultrasonic energy. After exemplarycomposite materials or laminates such as those referred to above areformed using an adhesive composition of the present invention, some orall of the composite or laminate may be exposed to ultrasonic energy.Referring to PCT International Publication Number WO 99/25296, which ishereby incorporated by reference in its entirety in a manner consistentwith the present document, the publication discloses the use ofultrasonic bonding to form side seams or seals in the disposableunderpant. (See, e.g., page 29, lines 10-25; additional detail regardingthe forming of such side seals is disclosed in U.S. Pat. No. 4,610,681,which issued on Sep. 9, 1986 and is entitled “Disposable UnderpantsHaving Discrete Outer Seals,” and which is hereby incorporated byreference in a manner consistent herewith; and U.S. Pat. No. 4,641,381,which issued on Feb. 10, 1997 and is entitled “Disposable Underpants,Such as Infant's Training Pants and the Like,” which is alsoincorporated by reference in a manner consistent with the presentdocument.)

Thus, adhesives of the present invention, used to make laminates andcomposite materials, may be exposed to ultrasonic energy whenultrasonic-bonding equipment is used in subsequent processing steps(e.g., when the ultrasonic bonding equipment is used to form the seamsor seals in the disposable absorbent article as discussed above).

Specific examples of composite materials, laminates, and disposableabsorbent articles with which adhesives of the present invention may beutilized are disclosed in the following U.S. Patents and U.S. patentapplications: U.S. Pat. No. 4,798,603 issued Jan. 17, 1989, to Meyer etal.; U.S. Pat. No. 5,176,668 issued Jan. 5, 1993, to Bernadine; U.S.Pat. No. 5,176,672 issued Jan. 5, 1993, to Bruemmer et al; U.S. Pat. No.5,192,606 issued Mar. 9, 1993, to Proxmire et al.; U.S. Pat. No.4,940,464, entitled “Disposable Incontinence Garment or Training Pant”;U.S. Pat. No. 5,904,675, entitled “Absorbent Article With ImprovedElastic Margins and Containment System”; U.S. Pat. No. 5,904,672,entitled “Absorbent Article Having Improved Waist Region Dryness andMethod of Manufacture”; and U.S. Pat. No. 5,902,297, entitled “AbsorbentArticle Having a Collection Conduit.” Each of the preceding U.S. patentsis incorporated by reference in its entirety and in a manner consistentwith the present document. More specifically, the types of absorbentarticles in which the adhesives of the present invention may be usedinclude diapers, children's training pants, swim wear, incontinenceproducts, feminine care products, other personal care or health caregarments, including medical garments, or the like. It should beunderstood that the present invention is applicable to other structures,composites, or products incorporating adhesive compositions of thepresent invention.

Additional Detail on Representative Process-Control Embodiments

As discussed above, process-control systems may be used to control thevolumetric or mass flow rate of adhesive compositions of the presentinvention to a point of application (e.g., to a point of application ona substrate, layer, or web that will be used to make a laminate orcomposite material). Persons of ordinary skill in the art of processcontrol are familiar with the various process-control strategies,algorithms, and equipment used to control a process. Some of thepossible strategies that may be used to control a process includefeedback-control strategies (i.e., a process in which a variable to becontrolled is measured, the measured value is compared to a desiredvalue, and the difference between the measured value and the desiredvalue is transmitted to a feedback controller that force adjusts amanipulative variable to drive the measured variable back to the desiredvalue) (see, e.g., FIG. 4A); feedforward-control strategies (i.e., aprocess in which a disturbance entering a process is detected, and anappropriate change is made to a manipulative variable so that an outputvariable is held constant; see, e.g., FIG. 4B); and the like.

One example of a process-control system is depicted in FIG. 5. A sensormay be used to determine a signal S₁ corresponding to the variable to becontrolled, e.g. the volumetric or mass flow rate of adhesive beingsprayed or delivered in an adhesive-application unit operation 74. Thissignal may then be relayed electrically, pneumatically, hydraulically,or by other means to a transmitter 76, which converts the signal S₁ intoa control signal M₁. The transmitter transmits the control signal M₁ tothe controller 78.

After receiving the control signal M₁, the controller sends thecorresponding output signal R₁ to the control element 80. The controlelement, such as an electronic or pneumatic control valve, responds tothe output signal R₁ by opening or closing, thus effecting the desiredchange to the variable being manipulated, in this case the volumetric ormass flow rate of adhesive. Alternatively, the control element mighteffect a desired change to the speed at which a pump operates, therebycontrolling the mass or volumetric flow rate of adhesive.

As mentioned above, an air-pressure, electrical, pneumatic, or othersignal may be used to transmit information (e.g., the various signalsdiscussed in the preceding paragraphs) from one device to another (e.g.,from a sensor, to a transmitter, to a controller, to a control element,or to some combination of some or all of these). For example, thecontroller may be a device that converts a control signal into anequivalent air-pressure, electrical, pneumatic, or other output signal.This air-pressure, electrical, pneumatic or other output signal is sentfrom the controller to a control element that effects a change to thevariable being manipulated. If the output signal is an air-pressuresignal, the output signal will be transmitted to the control element viatubing. The control element, such as a pneumatic control valve, respondsto the output signal by opening or closing, thus effecting the desiredchange to the variable being manipulated. The control system may includemultiple valves: e.g., a two-valve system with one operating as aone-directional, open-or-shut valve and the other operating as aproportional valve. Alternatively, the output signal is converted intoan electrical signal. The output signal is relayed to the controlelement via metal wire or other electrical conductor. The controlelement, such as an electronic control valve, responds to the electricalsignal by opening or closing, thus effecting the desired change to thevariable being manipulated.

An operator may input a value directly to the controller to produce acontrol signal. For example, an operator may adjust a dial or otherinput device on a pneumatic, hydraulic, electronic, or other controllerto adjust the volumetric or mass flow rate of adhesive. The operatorselects a setting on the input device of the controller corresponding tothe flow rate desired by the operator. Typically the operator will havecalibrated the input device on the controller so that input-devicesettings each correspond to specific volumetric or mass flow ratevalues.

A general-purpose computer may be used in place of, or in addition to,the controller mentioned above. Typically a general-purpose computeremploys an input device, including, but not limited to, an alpha-numerickeyboard, mouse, joystick, stylus, touch screen, or some combination ofthese. Other devices which may be used to input data to the computerinclude, but are not limited to: devices for reading data stored onmagnetic media such as 3.5 inch “floppy disks” or fixed-drives; devicesfor reading data stored on optical media, such as CD-ROMs; devices forreading data transmitted over cables, including optical cables; anddevices for scanning and digitizing information on a document. Inaddition to the input devices like those mentioned above, ageneral-purpose computer usually includes a visual display fordisplaying data. Also, a general-purpose computer typically has a devicefor storing and retrieving data that is inputted to the computer.Devices for storing and retrieving data include, but are not limited to:a disk drive for reading data from, and storing data on, a 3.5 inch“floppy disk”; a hard disk or other fixed drive; a tape drive; or otherdevice capable of reading data from, and storing data on, magneticmedia.

A general-purpose computer may be adapted for use in controlling thevolumetric or mass flow rate of adhesive. Typically a general-purposecomputer comprises devices for data input, data storage, dataprocessing, data display, and data output, as discussed above. Forpurposes of controlling volumetric or mass flow rate, thegeneral-purpose computer may further comprise a set of instructionscomprising the following steps: reading the control signal M₁, thecontrol signal M₁ being transmitted to the computer in computer-readableform; correlating the control signal M₁ to an output signal R₁ andtransmitting the output signal R₁ to a control element. The controlelement, such as an electronic, hydraulic, pneumatic, or other controlvalve, responds to the output signal R₁ by opening or closing, thuseffecting the desired change to the variable being manipulated, in thisvolumetric or mass flow rate. Alternatively, the control element mayeffect desired changes to the speed at which a positive-displacement orother metering pump operates, thereby effecting desired changes to massor volumetric flow rates.

The above discussion provides exemplars of equipment and methods forcontrolling the amount of adhesive being conducted to a point ofapplication per unit time. It should be understood that other equipmentand methods used to force adjust the flow rate of an adhesive of thepresent invention to a control set point, operator-inputted value, orother desired value falls within the scope of the present invention.

Tests/Procedures

Laminate Production

Laminates were made on equipment available from J & M Laboratories, abusiness having offices located in Dawsonville, Ga. As depicted in FIG.6, a first substrate or first base material 102, such as a nonwoven web,was directed from its corresponding unwind stand (not shown) to thesurface of a 6-inch-diameter steel roll 104 and through a nip 106between the steel roll and a 4-inch-diameter rubber roll 110. A secondsubstrate or second base material, such as a second nonwoven web 108,was directed from its unwind stand (not shown) to the surface of therubber roll and through the nip. Typically, the equipment was operatedat a speed of 300 feet per minute.

The applicator 114 used to deposit the adhesive was positioned so thatthe face of the depicted nozzle, which was roughly parallel to thesurface of the web to which adhesive was first applied, was 1.5 inches116 from the surface of the web. Furthermore, the central axis of thedepicted nozzle, which is perpendicular to the web to which adhesive isfirst applied, was 8 inches 118 from a parallel axis that passes throughthe nip defined by the rubber and steel rolls.

From the discussion above, it should be understood that the substratesand the resulting laminate 700 generally moved in a machine direction702 (see FIG. 7A) during their preparation. FIG. 7A depicts a top viewof a portion of a laminate after it has been formed. A continuous bandof adhesive 703, whether it was applied using meltblowing, cycloidal,slot, or other application technique, is denoted by broken lines 705 and707. The adhesive is under the upper substrate of the is wound up in theform of a roll. The direction that is perpendicular to the machinedirection, but lying within the plane of the laminate, is denoted as thecross-machine direction 704. Typically the width of the formed laminate,width denoting the dimension parallel to the cross-machine direction,was about 4 inches 706. The width of the applied adhesive, again widthdenoting a dimension parallel to the cross-machine direction, typicallywas from about 0.5 inches to about 1 inch 708. Also, the band ofadhesive was generally applied such that it was substantially centeredin the laminate (in the width dimension). Unless otherwise noted, thewidth of the applied adhesive was about 0.5 inches. (Note: the lines 710and 712 denote the manner in which a 2-inch 714 sample was cut forsubsequent analysis; sample preparation and orientation is discussed inmore detail below).

The selected adhesive was either an adhesive of the present invention(as noted in the Examples below), or a hot-melt adhesive (again as notedin the Examples below). The adhesive was added using a variety ofpatterns, including a meltblown pattern, a swirl or cycloidal pattern,or a pattern resulting from slot coating. Typically the adhesives wereheated to temperatures ranging from about 350 degrees Fahrenheit toabout 380 degrees Fahrenheit prior to application to one of thesubstrates. Unless otherwise noted, the selected adhesive was addedusing a meltblown pattern. As stated above, unless otherwise noted thewidth of the added adhesive was about 1.0 inch. The selected adhesivewas added in amounts varying from about 5 grams per square meter toabout 30 grams per square meter, with specific application levels oradd-on levels noted in the examples.

A number of different substrates were used to prepare the laminates, asnoted in the Examples below. The substrates that were used included: anecked-bonded laminate (“NBL”), which generally comprised a polyethylenelayer sandwiched between two polypropylene, spunbonded layers; apolypropylene, spunbonded layer (“SB”); and an outercover (“OC”)comprising a polyethylene layer and a polypropylene, spunbonded layer.For tests where the performance of a laminate of the present inventionwas compared to the performance of a laminate prepared using aconventional hot-melt adhesive, the same substrates were used to prepareboth the laminate of the present invention and the conventionallaminate.

180° Static Peel Test

The 180° static peel test was used to determine the approximate time tofailure of a laminate in which one substrate was adhesively bonded toanother substrate. All laminates were made as described above on a J & Mmachine. Samples were cut from the prepared laminate which, was in theform of a continuous web prepared on a J & M machine, as shown in FIG.7A. FIG. 7B depicts a sectional view of a sample that has been removedfrom the laminate depicted in FIG. 7A. The test procedure was conductedas follows: 1. A 2-inch test panel was cut from the laminate, as shownin FIGS. 7A and 7B. 2. The test laminate was then suspended verticallyin a forced-air oven, model number OV-490A-2 manufactured by Blue M Co.,a business having offices in Blue Island, Ill., that had been pre-heatedto a temperature of 100 degrees Fahrenheit, with the top of onesubstrate layer 750 secured by a clamp or other mechanical securingelement, the clamp or securing element having a width greater than 2inches. 3. A 500-gram weight was then affixed to the top edge 752 of theother substrate using a clamp or other mechanical securing element.Again, the clamp or securing element used to attach the 500-gram weightwas wider than 2 inches. 4. Approximately every ½ hour, the testlaminate was visually examined by quickly opening the oven door. Thetime at which one substrate or layer had detached from the othersubstrate or layer was recorded. The recorded time corresponded to theapproximate time of failure of the laminate. The two, now separate,substrates were then examined to determine the nature of the failure. Ifthe substrates separated such that most of the adhesive remained on oneof the substrates, then failure was deemed to be an adhesion failure(i.e., failure likely occurred at the interface between one of thesubstrates and the adhesive composition). If the substrates separatedsuch that adhesive remained on both substrates, the failure was deemedto be a cohesion failure (i.e., separation likely occurred within theadhesive composition itself). If neither of these conditions arose, butinstead one or both of the substrates failed (i.e., that portion of thelaminate bonded by the adhesive, usually a 1.0 inch by 2 inch area ofthe test panel), then the failure was deemed a material failure of oneor both substrates.

Dynamic Peel and Shear Testing

To determine dynamic peel strength, a laminate was tested for themaximum amount of tensile force that was needed to pull apart the layersof the laminate. Values for peel strength were obtained using aspecified width of laminate (for the present application, 2 inches);clamp jaw width (for the present application, a width greater than 2inches); and a constant rate of extension (for the present application,a rate of extension of 300 millimeters per minute). For samples having afilm side, the film side of the specimen is covered with masking tape,or some other suitable material, in order to prevent the film fromripping apart during the test. The masking tape is on only one side ofthe laminate and so does not contribute to the peel strength of thesample. This test uses two clamps, each clamp having two jaws with eachjaw having a facing in contact with the sample, to hold the material inthe same plane, usually vertically. The sample size is 2 inches (10.2cm) wide by 4 inches (20.4 cm). The jaw facing size is 0.5 inch (1.25cm) high by at least 2 inches (10.2 cm) wide, and the constant rate ofextension is 300 mm/mm. For a dynamic peel test, one clamp is attachedto the top 750 of one substrate of a test panel (see FIG. 7B). The otherclamp is attached to the top 752 of the other substrate of a test panel.During testing, the clamps move apart at the specified rate of extensionto pull apart the laminate. The sample specimen is pulled apart at 180degrees angle of separation between the two layers, and the peelstrength reported is the maximum tensile strength, in grams per inch,recorded during the test. Each of the peel strengths reported below isan average of five to nine tests. A suitable device for determining thepeel strength testing is a SINTECH 2 tester, available from the SintechCorporation, a business having offices at 1001 Sheldon Dr., Cary, N.C.27513; or an INSTRON Model TM, available from the Instron Corporation, abusiness having offices at 2500 Washington St., Canton, Mass. 02021; orthe Thwing-Albert Model INTELLECTII available from the Thwing-AlbertInstrument Co., a business having offices at 10960 Dutton Rd.,Philadelphia, Pa. 19154.

For a dynamic shear test, the procedure is as described above exceptthat one clamp is attached to the top 750 of one substrate of thelaminate, and the other clamp is attached to the bottom 754 of the othersubstrate of the laminate. The shear strength reported is the maximumtensile strength, in grams per square inch, recorded during the test.Each of the shear strengths reported is an average of five to ninetests.

Molecular Weight (Number Average and Weight Average)

A crystalline polypropylene was sent to American Polymer Standard Corp.,a business having offices in Philadelphia, Pa., for molecular-weightdeterminations. The number-average and/or weight-average molecularweights were determined by American Polymer using gel-permeationchromatography on a Waters Model No. 150 gel-permeation chromatograph.The determinations were made using: four, linear, Shodex GPC gelcolumns; poly(styrene-divinyl benzene) copolymers as standards;trichlorobenzene as the solvent, introduced to the chromatograph at avolumetric flow rate of 1.0 milliliter per minute; an operatingtemperature of 135 degrees Celsius; a sample-injection volume of 100microliters; an M-150C-(64/25) detector; and a GPC PRO 3.13 IBM AT datamodule.

EXAMPLES

Bonding strengths, i.e., dynamic shear and peel, as well as static peel,were determined for a blend of 20% crystalline polypropylene and 80%APAO, and also for a control of 100% APAO. The APAO used was REXTAC®2730, or RT 2730, available from Huntsman Corporation, Salt Lake City,Utah. Crystalline polypropylene, more specifically isotacticpolypropyelen, was obtained from Sigma-Aldrich in the form of white,spherical particles. The crystalline polypropylene was determined tohave a number-average molecular weight of about 15,000 and aweight-average molecular weight of about 110,000. The procuredcrystalline polypropylene had a melting index of 1000 grams per tenminutes (at a temperature of 230 degrees Celsius and when subjected to aforce of 2.16 kg; see ASTM D 1238, which was used for thisdetermination, for additional detail on measuring the melting index).

A first series of control samples were prepared by adhesively bondingtwo layers of substrate together using 100% RT 2730 melt-blown onto oneof the substrates at various concentrations prior to nipping the twosubstrates together with the adhesive located between the twosubstrates. A first series of test samples were prepared by adhesivelybonding two layers of substrate together using 20% crystallinepolypropylene and 80% RT 2730 melt-blown onto one of the substrates atvarious concentrations prior to nipping the two substrates together withthe adhesive located between the two substrates. A second series ofcontrol samples were prepared by adhesively bonding two layers ofsubstrate together using 100% RT 2730 applied in swirls on one of thesubstrates at various concentrations prior to nipping the two substratestogether with the adhesive located between the two substrates. A secondseries of test samples were prepared by adhesively bonding two layers ofsubstrate together using 20% crystalline polypropylene and 80% RT 2730applied in swirls on one of the substrates at various concentrationsprior to nipping the two substrates together with the adhesive locatedbetween the two substrates.

In each of the series of control samples and test samples, one sampleincluded two necked-bonded laminate (“NBL”) substrates with the adhesiveapplied at 10 grams per square meter (gsm). Each NBL layer was made upof a polyethylene layer sandwiched between two polypropylene, spunbondedlayers. A second sample in each of the series of control samples andtest samples included two NBL substrates with the adhesive applied at 15gsm. A third sample in each of the series of control samples and testsamples included a polypropylene, spunbonded layer (“SB”) and anoutercover (“OC”) comprising a polyethylene layer and a polypropylene,spunbonded layer, with the adhesive applied at 2.0 gsm in the melt-blownsamples and at 1.0 gsm in the swirl application samples.

Test results of the dynamic shear strength, dynamic peel strength, andstatic peel strength for the first series of control samples are shownin Table 1; test results for the first series of test samples are shownin Table 2; test results for the second series of control samples areshown in Table 3; and test results for the second series of test samplesare shown in Table 4.

For each of the control samples and each of the test samples, thedynamic shear strength was determined as described above (i.e., oneclamp was attached to the top of one substrate of the laminate, and theother clamp was attached to the bottom of the other substrate of thelaminate, and the clamps were pulled apart at a constant rate ofextension of 300 millimeters per minute).

For each of the control samples and each of the test samples, thedynamic peel strength was determined as described above (i.e., one clampwas attached to the top of one substrate of the laminate, and the otherclamp was attached to the top of the other substrate of the laminate,and the clamps were pulled apart at a constant rate of extension of 300millimeters per minute).

For each of the control samples and each of the test samples, the staticpeel strength was determined as described above (i.e., a 500 gram masswas attached to the upper edge of one of the substrates, with the testpanel suspended in an oven at a temperature of 75 degrees Fahrenheit).

TABLE 1 Bonding Strength of Melt-Blown Control Adhesive (100% RT 2730)Add-on/ Dynamic Shear Dynamic Peel Application (g/in²) (g/in) StaticPeel NBL/NBL, 3340 740 5 min 10 gsm (NBL delaminated) (Cohesion failure)NBL/NBL, — 800 15 min 15 gsm (Cohesion failure) OC/SB,  850 310 <2 min2.0 gsm (SB broke) (Cohesion failure)

TABLE 2 Bonding Strength of Melt-Blown Test Adhesive (20% CrystallinePolypropylene/80% RT 2730) Add-on/ Dynamic Shear Dynamic PeelApplication (g/in²) (g/in) Static Peel NBL/NBL, 3500 750 >48 hours 10gsm (NBL delaminated) (NBL delaminated) NBL/NBL, 3470 860 >72 hours 15gsm (NBL delaminated) (NBL delaminated) OC/SB, 1070 350 ˜10 min 2.0 gsm(SB broke) (OC delaminated)

TABLE 3 Bonding Strength of Swirled Control Adhesive (100% RT 2730)Add-on/ Dynamic Shear Dynamic Peel Application (g/in²) (g/in) StaticPeel NBL/NBL, 2070 380 1 min 10 gsm (NBL delaminated) (Cohesion failure)NBL/NBL, — 560 5 min 15 gsm (Cohesion failure  &  NBL delaminated)OC/SB,  790 100 <1 min 1.0 gsm (SB broke) (Cohesion failure)

TABLE 4 Bonding Strength of Swirled Test Adhesive (20% CrystallinePolypropylene/80% RT 2730) Add-on/ Dynamic Shear Dynamic PeelApplication (g/in²) (g/in) Static Peel NBL/NBL, 3590 870 ˜24 hours 10gsm (NBL delaminated) (NBL delaminated) NBL/NBL, — 990 >72 hours 15 gsm(NBL delaminated) OC/SB,  880 300 ˜10 min 1.0 gsm (SB broke) (OCdelaminated)

As can be seen by comparing Table 1 to Table 2, and Table 3 to Table 4,the bonding strength of the blend of crystalline polypropylene and RT2730 is considerably greater than the bonding strength of the RT 2730alone, in terms of dynamic shear strength, dynamic peel strength, andstatic peel strength, in each of the samples. The improved bondingstrength is particularly noticeable in the swirl applications.

Another observation that is apparent from Tables 2 and 4 is that thedynamic shear bond strength in laminates bonded with the blend ofcrystalline polypropylene and RT 2730 is greater than the dynamic shearmaterial strength of the substrates. More specifically, the testsresulted in either delamination of the NBL or breakage of the SB, ratherthan cohesion failure. Similarly, Tables 2 and 4 also show that thestatic peel bond strength in laminates bonded with the blend ofcrystalline polypropylene and RT 2730 is greater than the static peelmaterial strength of the substrates. More specifically, the testsresulted in delamination of either the NBL or the OC, rather thancohesion failure.

The remarkable difference between bonding strength of the blend and RT2730 alone may be attributed to forming a crystal domain of thecrystalline polypropylene. The crystal domain of the crystallinepolypropylene generates physical cross-linking in the matrix of theAPAO. The remarkably improved performance of bonding strength of theblend in the swirl application compared to melt-blown may be due to alarger ratio of mass of blend to bonding area in the swirl applicationthan that of melt-blown, thus resulting in more crystallization.

It will be appreciated that details of the foregoing embodiments, givenfor purposes of illustration, are not to be construed as limiting thescope of this invention. Although only a few exemplary embodiments ofthis invention have been described in detail above, those skilled in theart will readily appreciate that many modifications are possible in theexemplary embodiments without materially departing from the novelteachings and advantages of this invention. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention, which is defined in the following claims and all equivalentsthereto. Further, it is recognized that many embodiments may beconceived that do not achieve all of the advantages of some embodiments,particularly of the preferred embodiments, yet the absence of aparticular advantage shall not be construed to necessarily mean thatsuch an embodiment is outside the scope of the present invention.

What is claimed is:
 1. A pressure sensitive hot melt adhesive comprisingfrom about 70% to about 90% amorphous polyalphaolefin and from about 10%to about 30% crystalline polypropylene having a degree of crystallinityof at least about 40%, said amorphous polyalphaolefin comprising abutene-1 terpolymer with ethylene and propylene.
 2. The adhesivecomposition of claim 1, comprising between about 73% and about 87% ofthe amorphous polyalphaolefin, and between about 13% and about 27% ofthe crystalline polypropylene.
 3. The adhesive composition of claim 1,comprising between about 75% and about 85% of the amorphouspolyalphaolefin, and between about 15% and about 25% of the crystallinepolypropylene.
 4. The adhesive composition of claim 1, wherein thedegree of crystallinity of the crystalline polypropylene is at leastabout 60%.
 5. The adhesive composition of claim 1, wherein the degree ofcrystallinity of the crystalline polypropylene is at least about 80%. 6.The adhesive composition of claim 1, wherein the amorphouspolyalphaolefin has a number-average molecular weight between about5,000 and about 30,000.
 7. The adhesive composition of claim 1, whereinthe amorphous polyalphaolefin has a weight-average molecular weightbetween about 20,000 and about 60,000.
 8. The adhesive composition ofclaim 1, wherein the crystalline polypropylene has a number-averagemolecular weight between about 3,000 and about 200,000.
 9. The adhesivecomposition of claim 1, wherein the crystalline polypropylene has anumber-average molecular weight between about 10,000 and about 100,000.10. The adhesive composition of claim 1, wherein the adhesivecomposition has a melt index between about 200 and about 2000 grams per10 minutes.
 11. The adhesive composition of claim 1, wherein theadhesive composition has a melt index between about 400 and about 1800grams per 10 minutes.
 12. The adhesive composition of claim 1, whereinthe adhesive composition has a melt index between about 500 and about1500 grams per 10 minutes.
 13. The adhesive of claim 1 wherein thebutene-1 terpolymer comprises between about 20% and about 65% by weightbutene-1.
 14. The adhesive of claim 1 wherein the butene-1 terpolymercomprises between about 30% and about 55% by weight butene-1.
 15. Theadhesive composition of claim 1, wherein the crystalline polypropylenecomprises at least one of the group consisting of isotacticpolypropylene, syndiotactic polypropylene, and combinations thereof.